Just e-filed my return. I see it shows pending and acceptance date 24-48 hours. Should I print and mail tomorrow instead so it has the postmark of 10/17?

No.   If you e-filed you have five days to fix it and re-file if it is rejected.   If you still cannot e-file successfully, then you can print out a copy of the e-file rejection and include it with your mailed tax return.

And...in the event that it is rejected, most rejections are for AGI.   If your return is rejected for AGI the "fix" is often to just use zero as your 2020 AGI and re-file.